Hose assemblies for conveying fuel and other corrosive materials are well known in the art. Such assemblies are exposed to a variety of fuel mixtures, fuel additives, and caustic materials in addition to being exposed to extreme temperatures and environments. Thus, such hose assemblies must be resistant to chemical, environmental, and physical degradation resulting from chemical exposure, environmental exposure to heat, and physical degradation resulting from bending and repeated movement or forces applied to the hose.
Polymeric fluorocarbon materials, such as polytetrafluorethylene, possess the requisite chemical and temperature resistant properties for most fuel hose applications. Unfortunately, in addition to being expensive, polymeric fluorocarbon materials exhibit relatively poor tensile and hoops strengths. As a result, fluorocarbon materials are prone to kinking. Also, because of inherent memory by the materials, such kinking remains permanent and provides both continual resistance to fluid flow through the hose assembly and also weakens the integrity of the hose assembly. Moreover, as a result of the low tensile strength, the attachment or fixation of coupling members to hose assemblies is difficult.
Various approaches have been described for imparting additional strength to a polymeric fluorocarbon liner. One such approach involves braiding fibers about the inner fluorocarbon liner. The braided fibers provide additional strength to the fluorocarbon liner which results in a hose assembly that resists kinking. Examples of such approaches are disclosed in U.S. Pat. Nos. 5,124,878 issued Jun. 23, 1992, 5,142,782, issued Sep. 1, 1992, and 5,192,476 issued Mar. 9, 1993, all assigned to the assignee of the present invention.
The hose assembly described in the '878 patent includes an extruded and seamless smooth bore inner polymeric fluorocarbon liner, a braided reinforcing layer disposed about the exterior of the inner liner and includes an organic polymeric material dispersed in the reinforcing layer which connects the reinforcing layer to the inner liner thereby providing a hose assembly which is extremely strong and kink resistant.
U.S. Pat. No. 5,170,011, issued Dec. 8, 1992, and reissued as U.S. Pat. No. RE35,527, issued Jun. 10, 1997, and assigned to the assignee of the present invention, discloses a hose assembly including an extruded polymeric fluorocarbon inner liner and a polyamide outer liner disposed about the inner liner which can either be expanded or unexpanded. The advantage of this hose assembly is that when an expanded polyamide material is utilized for the outer liner, a substantial reduction in both the weight and the cost of the hose assembly is achieved while maintaining the necessary strength of the hose. Additionally, when an expanded polyamide liner is utilized, the expanded polyamide outer liner provides protection from external heat and chemical degradation at a substantially reduced weight.
U.S. Pat. No. 5,613,524, issued Mar. 25, 1997, discloses a lightweight hose assembly including an extruded polymeric fluorocarbon inner liner and an outer foamed layer of polymeric fluorocarbon material. The hose assembly can also include a reinforcing layer disposed either about the inner liner or about the outer layer. The hose assembly is lightweight, strong, and kink resistant. The use of a foamed fluorocarbon disposed over the smooth bore extruded inner liner minimizes the use of the expensive fluorocarbon material by imparting close cell voids within the fluorocarbon material thus requiring less material to form the outer layer. As is well known in the art, polymeric fluorocarbon materials are extremely expensive and the use of the expanded fluorocarbon outer layer represented an advance in reducing the cost of the hose assembly. Additionally, the use of the expanded or foamed fluorocarbon outer layer provides an excellent substrate for the attachment of end fittings to the hose assembly by various means including crimping or screw clamping.
As was immediately pointed out above, expanded fluorocarbon polymeric materials have been utilized in the construction and design of hose assemblies. However, expanded or foamed fluorocarbon layers have only been disposed about a smooth bore extruded fluorocarbon inner liner. Until now, the extrusion of an expanded or foamed fluorocarbon tube itself has not been done. The primary reason for the lack of a tube or hose assembly including an expanded fluorocarbon inner liner has been the inability to extrude an expanded fluorocarbon inner liner as it was thought that the expanded fluorocarbon material could not stand up to the then current methods for extrusion of an expanded material.
In general, expanded fluorocarbon products, such as fluorocarbon insulated wire and hoses having an expanded fluorocarbon layer disposed over a solid unexpanded fluorocarbon layer, were some of the only products known to utilize an expanded fluorocarbon material. However, these expanded fluorocarbon layers could only be extruded over a solid substrate such as a wire or an extruder, non-expanded inner liner.
As pointed out above, the use of smooth bore extruded, non-expanded fluorocarbon inner liners is expensive due to the amount of fluorocarbon material necessary to extrude an inner fluorocarbon liner having a wall thick enough to carry the pressures of the fluid flowing therein, capable of being attached to an end fitting without kinking or failure, and allowing for the use of various methods of attaching end fittings to the hose assembly. Therefore, it would be desirable to have an expanded polymeric fluorocarbon tube and/or hose assembly which allows for the utilization of less of the expensive fluorocarbon polymer material, is flexible, kink resistant, less expensive, and which eliminates the disadvantages of the hose assemblies described above. Furthermore, it would be desirable to have a method for extruding an expanded fluorocarbon tube and also utilizing the tube in a hose assembly having, an expanded polymeric fluorocarbon material as its fluid carrying member. Additionally, it would be desirable to have an expanded polymeric fluorocarbon tube in which, because the material is expanded, a heavier wall thickness is possible without increasing the cost of producing the tube or hose assembly which allows for the more positive attachment of end fittings and also for a variety of methods for attaching end fittings to be utilized. This positive attachment can reduce the problem known as creep. Additionally, since the tube or hose assembly is constructed of a closed cell material, it possesses good insulative properties and can be used to carry fluid and/or provide insulation from extreme temperatures, such as being used as a heat shield.
Additionally, by utilizing a melt extrudable fluoropolymer, the expanded tube or hose assembly is heat foamable and can be bent into any desired shape or configuration.